This is the spine or the fin on the top of the fish connected to the spine. The fin comes in a vast array of shapes and sizes. In some fish there appear to be two dorsal fins, the largest will be the main "spiny" dorsal fin, the smaller one towards the back of the fin is named the "soft" dorsal fin or "adipose" fin. In some fish the dorsal fin can be absent. The adipose fin is always present in Characins, never present in Cyprinids.

A pair of fins also known as the ventral fins. One fin is found on each side of the body, positioned on the ventral surface between the head and the vent. On some species of fish it is not present. On some fish such as the Betta splenden there are elongated ventral fins, with fish such as Gourami these can act as "feelers".

One fin on the ventral surface of the fish. This is usually always positioned after the vent at the rear of the fish just before the Caudal fin. In some species of male livebearers (Mollies for example) this fin is modified to act as a sperm depositor called a Gonopodium. The fin has a small hook on the and the male can flick this fin forward to latch onto the female.

The tail. In some species of fish this can be connected, or appear connected, to the anal fin. The Caudal peduncle refers to the base of the caudal where it connects to the body. If the tail is forked, each part of the fin will be referred to as the lobe.

This is of course the essential part of the fish, it is what makes it possible for them to breath. The gills on some fish are more prominent than others. Occasionally words such as Opercle can be used to describe this area of the fish, this means the uppermost and largest of the bones that form the gill cover.